America's top national security threat

By Clark K. Ervin

Updated 8:03 PM ET, Thu September 10, 2015

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Photos:The ISIS terror threat

Wounded passengers are treated following a suicide bombing at the Brussels Airport on March 22, 2016. The attacks on the airport and a subway killed 32 people and wounded more than 300. ISIS claims its "fighters" launched the attacks in the Belgian capital.

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Photos:The ISIS terror threat

Syrians gather at the site of a double car bomb attack in the Al-Zahraa neighborhood of the Homs, Syria, on February 21, 2016. Multiple attacks in Homs and southern Damascus kill at least 122 and injure scores, according to the state-run SANA news agency. ISIS claimed responsibility.

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Photos:The ISIS terror threat

Syrian pro-government forces gather at the site of a deadly triple bombing Sunday, January 31, in the Damascus suburb of Sayeda Zeynab. ISIS claimed responsibility for the attack, according to a statement circulating online from supporters of the terrorist group.

Wounded people are helped outside the Bataclan concert hall in Paris following a series of coordinated attacks in the city on Friday, November 13. The militant group ISIS claimed responsibility for the attacks, which killed at least 130 people and wounded hundreds more.

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Photos:The ISIS terror threat

Emergency personnel and civilians gather at the site of a twin suicide bombing in Beirut, Lebanon, on Thursday, November 12. The bombings killed at least 43 people and wounded more than 200 more. ISIS appeared to claim responsibility in a statement posted on social media.

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Photos:The ISIS terror threat

Smoke rises over the northern Iraqi town of Sinjar on November 12. Kurdish Iraqi fighters, backed by a U.S.-led air campaign, retook the strategic town, which ISIS militants overran last year. ISIS wants to create an Islamic state across Sunni areas of Iraq and Syria.

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Photos:The ISIS terror threat

Syrian government troops walk inside the Kweiras air base on Wednesday, November 11, after they broke a siege imposed by ISIS militants.

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Photos:The ISIS terror threat

Members of the Egyptian military approach the wreckage of a Russian passenger plane Sunday, November 1, in Hassana, Egypt. The plane crashed the day before, killing all 224 people on board. ISIS claimed responsibility for downing the plane, but the group's claim wasn't immediately verified.

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Photos:The ISIS terror threat

An explosion rocks Kobani, Syria, during a reported car bomb attack by ISIS militants on Tuesday, October 20.

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Photos:The ISIS terror threat

Shiite fighters, fighting alongside Iraqi government forces, fire a rocket at ISIS militants as they advance toward the center of Baiji, Iraq, on Monday, October 19.

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Photos:The ISIS terror threat

Smoke rises above a damaged building in Ramadi, Iraq, following a coalition airstrike against ISIS positions on Saturday, August 15.

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Photos:The ISIS terror threat

Iraqi men look at damage following a bomb explosion that targeted a vegetable market in Baghdad on Thursday, August 13. ISIS claimed responsibility for the attack.

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Photos:The ISIS terror threat

In this image taken from social media, an ISIS fighter holds the group's flag after the militant group overran the Syrian town of al-Qaryatayn on Thursday, August 6, the London-based Syrian Observatory for Human Rights reported. ISIS uses modern tools such as social media to promote reactionary politics and religious fundamentalism. Fighters are destroying holy sites and valuable antiquities even as their leaders propagate a return to the early days of Islam.

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Photos:The ISIS terror threat

An ISIS fighter poses with spoils purportedly taken after capturing the Syrian town of al-Qaryatayn.

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Photos:The ISIS terror threat

Smoke rises as Iraqi security forces bomb ISIS positions in the eastern suburbs of Ramadi, Iraq, on August 6.

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Photos:The ISIS terror threat

Buildings reduced to piles of debris can be seen in the eastern suburbs of Ramadi on August 6.

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Photos:The ISIS terror threat

The governor of the Asir region in Saudi Arabia, Prince Faisal bin Khaled bin Abdulaziz, left, visits a man who was wounded in a suicide bombing attack on a mosque in Abha, Saudi Arabia, on August 6. ISIS claimed responsibility for the explosion, which killed at least 13 people and injured nine others.

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Photos:The ISIS terror threat

Saudi officials and investigators check the inside of the mosque on August 6.

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Photos:The ISIS terror threat

Mourners in Gaziantep, Turkey, grieve over a coffin Tuesday, July 21, during a funeral ceremony for the victims of a suspected ISIS suicide bomb attack. That bombing killed at least 31 people in Suruc, a Turkish town that borders Syria. Turkish authorities blamed ISIS for the attack.

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Photos:The ISIS terror threat

Protesters in Istanbul carry anti-ISIS banners and flags to show support for victims of the Suruc suicide blast during a demonstration on Monday, July 20.

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Photos:The ISIS terror threat

People in Ashmoun, Egypt, carry the coffin for 1st Lt. Mohammed Ashraf, who was killed when the ISIS militant group attacked Egyptian military checkpoints on Wednesday, July 1. At least 17 soldiers were reportedly killed, and 30 were injured.

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Photos:The ISIS terror threat

Syrians wait near the Turkish border during clashes between ISIS and Kurdish armed groups in Kobani, Syria, on Thursday, June 25. The photo was taken in Sanliurfa, Turkey. ISIS militants disguised as Kurdish security forces infiltrated Kobani on Thursday and killed "many civilians," said a spokesman for the Kurds in Kobani.

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Photos:The ISIS terror threat

Residents examine a damaged mosque after an Iraqi Air Force bombing in the ISIS-seized city of Falluja, Iraq, on Sunday, May 31. At least six were killed and nine others wounded during the bombing.

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Photos:The ISIS terror threat

People search through debris after an explosion at a Shiite mosque in Qatif, Saudi Arabia, on Friday, May 22. ISIS claimed responsibility for the attack, according to tweets from ISIS supporters, which included a formal statement from ISIS detailing the operation.

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Photos:The ISIS terror threat

Iraqi soldiers fire their weapons toward ISIS group positions in the Garma district, west of the Iraqi capital of Baghdad, on Sunday, April 26. Pro-government forces said they had recently made advances on areas held by Islamist jihadists.

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Photos:The ISIS terror threat

A member of Afghanistan's security forces stands at the site where a suicide bomber on a motorbike blew himself up in front of the Kabul Bank in Jalalabad, Afghanistan, on Saturday, April 18. ISIS claimed responsibility for the attack. The explosion killed at least 33 people and injured more than 100 others, a public health spokesman said.

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Photos:The ISIS terror threat

Iraqi counterterrorism forces patrol in Ramadi on April 18.

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Photos:The ISIS terror threat

Thousands of Iraqis cross a bridge over the Euphrates River to Baghdad as they flee Ramadi on Friday, April 17.

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Photos:The ISIS terror threat

Yazidis embrace after being released by ISIS south of Kirkuk, Iraq, on Wednesday, April 8. ISIS released more than 200 Yazidis, a minority group whose members were killed, captured and displaced when the Islamist terror organization overtook their towns in northern Iraq last summer, officials said.

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Photos:The ISIS terror threat

Kurdish Peshmerga forces help Yazidis as they arrive at a medical center in Altun Kupri, Iraq, on April 8.

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Photos:The ISIS terror threat

A Yazidi woman mourns for the death of her husband and children by ISIS after being released south of Kirkuk on April 8. ISIS is known for killing dozens of people at a time and carrying out public executions, crucifixions and other acts.

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Photos:The ISIS terror threat

People in Tikrit inspect what used to be a palace of former President Saddam Hussein on April 3.

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Photos:The ISIS terror threat

On April 1, Shiite militiamen celebrate the retaking of Tikrit, which had been under ISIS control since June. The push into Tikrit came days after U.S.-led airstrikes targeted ISIS bases around the city.

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Photos:The ISIS terror threat

Iraqi security forces launch a rocket against ISIS positions in Tikrit on Monday, March 30.

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Photos:The ISIS terror threat

The parents of 19-year-old Mohammed Musallam react at the family's home in the East Jerusalem Jewish settlement of Neve Yaakov on Tuesday, March 10. ISIS released a video purportedly showing a young boy executing Musallam, an Israeli citizen of Palestinian descent who ISIS claimed infiltrated the group in Syria to spy for the Jewish state. Musallam's family told CNN that he had no ties with the Mossad, Israel's spy agency, and had, in fact, been recruited by ISIS.

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Photos:The ISIS terror threat

Iraqi Shiite fighters cover their ears as a rocket is launched during a clash with ISIS militants in the town of Al-Alam, Iraq, on Monday, March 9.

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Photos:The ISIS terror threat

Displaced Assyrian women who fled their homes due to ISIS attacks pray at a church on the outskirts of Damascus, Syria, on Sunday, March 1. ISIS militants abducted at least 220 Assyrians in Syria.

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Photos:The ISIS terror threat

Safi al-Kasasbeh, right, receives condolences from tribal leaders at his home village near Karak, Jordan, on Wednesday, February 4. Al-Kasasbeh's son, Jordanian pilot Moath al-Kasasbeh, was burned alive in a video that was recently released by ISIS militants. Jordan is one of a handful of Middle Eastern nations taking part in the U.S.-led military coalition against ISIS.

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Photos:The ISIS terror threat

A Kurdish marksman looks over a destroyed area of Kobani on Friday, January 30, after the city had been liberated from the ISIS militant group. The Syrian city, also known as Ayn al-Arab, had been under assault by ISIS since mid-September.

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Photos:The ISIS terror threat

Kurdish people celebrate in Suruc, Turkey, near the Turkish-Syrian border, after ISIS militants were expelled from Kobani on Tuesday, January 27.

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Photos:The ISIS terror threat

Collapsed buildings are seen in Kobani on January 27 after Kurdish forces took control of the town from ISIS.

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Photos:The ISIS terror threat

Junko Ishido, mother of Japanese journalist Kenji Goto, reacts during a news conference in Tokyo on Friday, January 23. ISIS would later kill Goto and another Japanese hostage, Haruna Yukawa.

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Photos:The ISIS terror threat

ISIS militants are seen through a rifle's scope during clashes with Peshmerga fighters in Mosul, Iraq, on Wednesday, January 21.

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Photos:The ISIS terror threat

An elderly Yazidi man arrives in Kirkuk after being released by ISIS on Saturday, January 17. The militant group released about 200 Yazidis who were held captive for five months in Iraq. Almost all of the freed prisoners were in poor health and bore signs of abuse and neglect, Kurdish officials said.

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Photos:The ISIS terror threat

Smoke billows behind an ISIS sign during an Iraqi military operation to regain control of the town of Sadiyah, about 95 kilometers (60 miles) north of Baghdad, on Tuesday, November 25.

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Photos:The ISIS terror threat

Fighters from the Free Syrian Army and the Kurdish People's Protection Units join forces to fight ISIS in Kobani on Wednesday, November 19.

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Photos:The ISIS terror threat

A picture taken from Turkey shows smoke rising after ISIS militants fired mortar shells toward an area controlled by Syrian Kurdish fighters near Kobani on Monday, November 3.

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Photos:The ISIS terror threat

Iraqi special forces search a house in Jurf al-Sakhar, Iraq, on Thursday, October 30, after retaking the area from ISIS.

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Photos:The ISIS terror threat

ISIS militants stand near the site of an airstrike near the Turkey-Syria border on Thursday, October 23. The United States and several Arab nations have been bombing ISIS targets in Syria to take out the militant group's ability to command, train and resupply its fighters.

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Photos:The ISIS terror threat

Kurdish fighters walk to positions as they combat ISIS forces in Kobani on Sunday, October 19.

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Photos:The ISIS terror threat

Heavy smoke rises in Kobani following an airstrike by the U.S.-led coalition on October 18.

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Photos:The ISIS terror threat

Cundi Minaz, a female Kurdish fighter, is buried in a cemetery in the southeastern Turkish town of Suruc on Tuesday, October 14. Minaz was reportedly killed during clashes with ISIS militants in nearby Kobani.

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Photos:The ISIS terror threat

Kiymet Ergun, a Syrian Kurd, celebrates in Mursitpinar, Turkey, after an airstrike by the U.S.-led coalition in Kobani on Monday, October 13.

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Photos:The ISIS terror threat

Alleged ISIS militants stand next to an ISIS flag atop a hill in Kobani on Monday, October 6.

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Photos:The ISIS terror threat

A Kurdish Peshmerga soldier who was wounded in a battle with ISIS is wheeled to the Zakho Emergency Hospital in Duhuk, Iraq, on Tuesday, September 30.

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Photos:The ISIS terror threat

Syrian Kurds wait near a border crossing in Suruc as they wait to return to their homes in Kobani on Sunday, September 28.

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Photos:The ISIS terror threat

A elderly man is carried after crossing the Syria-Turkey border near Suruc on Saturday, September 20.

Kurdish Peshmerga fighters fire at ISIS militant positions from their position on the top of Mount Zardak, east of Mosul, Iraq, on Tuesday, September 9.

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Photos:The ISIS terror threat

Displaced Iraqis receive clothes from a charity at a refugee camp near Feeshkhabour, Iraq, on Tuesday, August 19.

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Photos:The ISIS terror threat

Aziza Hamid, a 15-year-old Iraqi girl, cries for her father while she and some other Yazidi people are flown to safety Monday, August 11, after a dramatic rescue operation at Iraq's Mount Sinjar. A CNN crew was on the flight, which took diapers, milk, water and food to the site where as many as 70,000 people were trapped by ISIS. But only a few of them were able to fly back on the helicopter with the Iraqi Air Force and Kurdish Peshmerga fighters.

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Photos:The ISIS terror threat

Thousands of Yazidis are escorted to safety by Kurdish Peshmerga forces and a People's Protection Unit in Mosul on Saturday, August 9.

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Photos:The ISIS terror threat

Thousands of Yazidi and Christian people flee Mosul on Wednesday, August 6, after the latest wave of ISIS advances.

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Photos:The ISIS terror threat

A Baiji oil refinery burns after an alleged ISIS attack in northern Selahaddin, Iraq, on Thursday, July 31.

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Photos:The ISIS terror threat

A Syrian rebel fighter lies on a stretcher at a makeshift hospital in Douma, Syria, on Wednesday, July 9. He was reportedly injured while fighting ISIS militants.

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Photos:The ISIS terror threat

Children stand next to a burnt vehicle during clashes between Iraqi security forces and ISIS militants in Mosul on Tuesday, June 10.

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Story highlights

Ervin: 14 years after September 11, America still must be concerned about terrorist threat

He says al Qaeda, its affiliates, and ISIS all represent sources of danger to the U.S. homeland

Clark K. Ervin, who was the first inspector general of the Department of Homeland Security, is director of the Homeland Security Program at the Aspen Institute and a partner at the law firm Squire Patton Boggs. The opinions expressed in this commentary are his.

(CNN)The then-incoming Chairman of the Joint Chiefs of Staff, Gen. Joseph Dunford, made news at his confirmation hearing in July by saying that, in his view, Russia was now the greatest national security threat facing the United States.

Clark K. Ervin

Certainly, the chairman has a point.

There is no question but that Vladimir Putin is determined to do everything in his power to restore as much of the Soviet empire as possible and to do everything in his power to "stick it to" the United States, in general, and to President Obama, in particular, whom he views as weak and indecisive.

There are other contenders for the dubious title of "No. 1 Security Threat to the United States." China, Iran, and North Korea come to mind, for reasons that are obvious to even the most casual observers of national security issues and foreign policy.

But, to my mind, 14 years after 9/11, there is no question but that the No. 1 security threat to the nation remains terrorism. Unlike Russia and China, which are long-term threats to America's continued global geopolitical hegemony, and unlike Iran and North Korea, which are near-term threats to our regional allies and interests, terrorism is a direct and immediate threat to the United States itself, to our very "homeland."

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Photos:Photos: America remembers 9/11

Photos:Photos: America remembers 9/11

America remembers 9/11 – Kellen Savoy, center, helps present the colors as students raise the flag at William Lloyd Meador Elementary School in Willis, Texas, on September 11, 2013, during a ceremony in observance of the 9/11 terrorist attacks. Observances were held at the sites of the attacks that killed nearly 3,000 people in Lower Manhattan, at the Pentagon and southwestern Pennsylvania in 2001. Tributes were also held across the United States:

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Photos:Photos: America remembers 9/11

America remembers 9/11 – Hector Garcia, center, of Brooklyn, and his daughter Tania attend ceremonies in New York on September 11. Garcia is carrying a photograph of his daughter Marilyn, Tania's sister, who died in the attacks on the World Trade Center.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – President Barack Obama listens to military taps after laying a wreath at the Pentagon in Arlington, Virginia, on September 11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – Family and friends of Wayne A. Russo attend ceremonies at the 9/11 Memorial in New York on September 11. Russo, an accountant for Marsh & McLennan, died while working in his office in the World Trade Center attacks on 9/11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – A group of men says prayers on September 11 in Raleigh, North Carolina, for those who died in the terror attacks.

America remembers 9/11 – Ester DiNardo, mother of Marisa DiNardo, clutches a photograph of her daughter at the 9/11 Memorial ceremonies in New York.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – A pool at the 9/11 Memorial in New York reflects surrounding buildings during ceremonies for the 12th anniversary of the terrorist attacks.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – People gather in front of the Pentagon in Arlington, Virginia, before an observance ceremony on September 11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – President Barack Obama, first lady Michelle Obama, Vice President Joe Biden and his wife, Jill Biden, observe a moment of silence on the South Lawn of the White House on September 11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – Daniel Henry, a police officer with the Port Authority of New York and New Jersey, pauses during a moment of silence at the south reflecting pool of the 9/11 Memorial in New York on September 11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – Mija Quigley of Princeton Junction, New Jersey, embraces the name of son Patrick Quigley at the 9/11 Memorial on September 11. He died aboard United Airlines Flight 175, which crashed into the World Trade Center on 9/11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – Showkatara Sharif stands next to the engraving of her daughter's name, Shakila Yasmin, at the edge of the north pool at the 9/11 Memorial in New York on September 11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – A man makes a rubbing of his friend's name, New York firefighter Vincent Giammona, at the south pool of the 9/11 Memorial on September 11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – The Tribute in Light marks the 12th anniversary of the 9/11 attacks on the evening of Tuesday, September 10, in New York.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – Visitors check out victims' names at the 9/11 Memorial in New York on September 10.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – A woman kisses one of the 40 names on the Flight 93 National Memorial wall in Shanksville, Pennsylvania, on September 10. United Airlines Flight 93 crashed into a field near Shanksville on 9/11.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – A woman takes photos of the 9/11 Memorial in New York on September 10.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – A girl poses among American flags that Pepperdine University students and staff erected in Malibu, California, on September 10.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – A beam from the World Trade Center is seen inside the 9/11 Museum in New York on September 10.

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Photos:Photos: America remembers 9/11

America remembers 9/11 – A flower lies atop names of victims at the 9/11 Memorial in New York on September 10.

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Photos:Photos: America remembers 9/11

Photos: America remembers 9/11 – Patriot Guard rider and U.S. Navy veteran Ron Connally, center, of Oak Harbor, Washington, holds a flag during a ceremony in Bremerton on September 11.

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Needless to say, the directness and immediacy of the threat was made catastrophically clear on 9/11, with the killing of thousands of Americans in New York and Washington that tragic day. All these many years later, the threat is just as direct and immediate. If anything, it is even more so.

For one thing, the terrorist group that perpetrated that attack, known in national security parlance nowadays as "al Qaeda core," is still with us. Yes, Osama bin Laden is dead, thankfully, and many other senior leaders in the years since 9/11 have likewise been killed or captured. Al Qaeda is but a shadow of its former self, but not all shadows are chimerical.

Al Qaeda is still out there, determined to carry out another 9/11-scale attack on the homeland. If anything, given the competition among terror groups now to be the "biggest and baddest," al Qaeda is more determined than ever to do so, to prove that it is still in the game and more potent than the other players on the field.

And, there are now menacing al Qaeda affiliates around the world, with the most menacing being, of course, its Yemeni branch, Al Qaeda in the Arabian Peninsula, or "AQAP." They are likewise determined to carry out another catastrophic attack on the homeland, and are particularly fixated on devising explosives that can evade detection and bring down airliners.

The goal seems to be to prove that, all these many years after 9/11, with huge resources and attention devoted to securing the aviation sector, we are still weak at our strongest point. But for the grace of God and strong intelligence partnerships, AQAP would have succeeded already.

But, now, added to the mix is the gravest terror threat of all, a group that is truly "sui generis," ISIS. What makes ISIS unique? Why does every other terror group, and every other national security threat, pale in comparison?

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First, it holds vast stretches of territory. And, this territory is not in some obscure, out of the way place like the Afghan/Pakistan border, where al Qaeda core makes its home. It is in Iraq and Syria, right in the heart of the Middle East and right on the periphery of Europe (which, of course, not incidentally, largely accounts for the huge migrant crisis in Europe now that, at least to some degree is a potential security threat in and of itself). ISIS can, and does use this territory to plot and train for terror attacks, and to showcase what jihadi governance is like, which is a recruiting tool in and of itself.

Second, it is immensely wealthy from captured oil refineries, taxation, and extortion. Al Qaeda had to depend on the generosity of Gulf donors, and, while still flowing, that pipeline has been increasingly clogged by the aggressive and creative efforts of counterterrorism experts in our Treasury Department.

Third, ISIS fighters are not some ragtag band of would be tough guys. The core of ISIS are the battle-hardened top ranks of Saddam's Baathist army. These guys know how to fight and to win.

Cheney was in his West Wing office when he received word that a plane had struck the World Trade Center. The released photos were requested by the coordinating producer for a group that has produced Bush administration films for PBS' "Frontline."

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Photos:Photos of Cheney, Bush from 9/11 released for first time

The photos capture the grim scenario facing the White House as commandeered airliners crashed into the World Trade Center, the Pentagon and a field in Pennsylvania. President George W. Bush, Cheney and staff gather at the President's Emergency Operations Center later in the day.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Colette Neirouz Hanna, who works with the Kirk Documentary Group, told the Boston Globe, "From the first moments after the attacks on the World Trade Center, Vice President Cheney has been at the center of much of the government's response. Now, 14 years later, we finally have those photographs and the American people can see for themselves what took place in those first 24 hours."

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Photos:Photos of Cheney, Bush from 9/11 released for first time

"Frontline," in an online posting on July 25, said the images were taken by Cheney's staff photographer. Cheney told CNN's John King in 2002 what happened when it was clear there was an ongoing terrorist operation. After he called President Bush in Florida and spoke with top aides his door burst open. "My [Secret Service] agent all of a sudden materialized right beside me and said, 'Sir, we have to leave now.' He grabbed me and propelled me out of my office, down the hall, and into the underground shelter in the White House," Cheney said.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Cheney with members of the White House staff, including National Security Adviser Condoleezza Rice. "Frontline" said Friday's release of photos was the second set requested by Hanna. That first set shows other behind-the-scenes photos of Bush and Cheney.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Lynne Cheney discusses the ongoing crisis with her husband, the vice president. According to a 2002 CNN article on the attack anniversary, Dick Cheney helped direct the U.S. government's response from an emergency bunker while the President was in Florida and flying to Nebraska for security reasons. Bush issued orders while in transit.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

According to historycommons.org, Bush arrived at the White House shortly before 7 p.m. on September 11. A few minutes later, he entered the Emergency Operations Center.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Cheney with National Security Adviser Condoleezza Rice in the President's Emergency Operations Center.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

A relic of the Cold War, the deep underground bunker became the vice president's base of operations on the first day of a new war.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Rice and Secretary of State Colin Powell confer during the crisis.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Mary Matalin, then a counselor to Cheney, said this of the Presidential Emergency Operations Center: "I didn't know that it existed until I was actually down there, and I'm not sure I could find my way back there to this day."

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Cheney with Laura Bush and Lynne Cheney. The latter was a constant presence. She leaned in at one point to tell the vice president that their daughters were fine.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Secretary of State Colin Powell looks over a report. All of the released photos are available in a National Archives Flickr album.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

After their reunion, the President and the first lady "talked with the Cheneys a bit," Laura Bush was to recall. President Bush then went upstairs to prepare for a nationally televised address.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

President Bush speaks with Vice President Cheney and members of his senior staff. The vice president had a few words with the president just before the latter's address to the nation. CIA Director George Tenet watched from the bunker, waiting for Bush to convene a late-night meeting of the National Security Council.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Mary Matalin talks with Karen Hughes, counselor to the President, near Lynne Cheney in the President's Emergency Operations Center.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Cheney talks with Secretary of Transportation Norman Mineta.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

CIA Director George Tenet listens to President Bush's televised address. The President said, "Terrorist attacks can shake the foundations of our biggest buildings, but they cannot touch the foundation of America. These acts shatter steel, but they cannot dent the steel of American resolve."

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Photos:Photos of Cheney, Bush from 9/11 released for first time

It was the bunker's first test in an actual emergency, a day of crisis with some hitches. Cheney wanted to track TV reports of the devastation and listen in on communications with the Pentagon. "You can have sound on one or the other and he found that technically imperfect," Matalin recalled.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

The Cheneys depart the White House and prepare to board Marine Two. He later took a nighttime ride past the heavily damaged Pentagon. "I recall watching the vice president, who was staring out the window at the Pentagon, and wondering what he may be thinking about, the responsibilities he would have in the future. A pretty sobering moment," said Libby, his chief of staff.

Cheney and Lynne Cheney arrive at Camp David. This was the first in a series of "undisclosed locations" where the vice president camped out in the weeks after the attacks, PBS said.

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Photos:Photos of Cheney, Bush from 9/11 released for first time

Cheney, shown here at Camp David on September 11, 2001. A year later, he recalled to CNN's John King: "As we lifted off and headed up the Potomac [River], you could look out and see the Pentagon, see that black hole where it'd been hit. A lot of lights on the building, smoke rising from the Pentagon. And you know, it really helped to bring home the impact of what had happened, that we had in fact been attacked."

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Fourth, needless to say, ISIS is savagely brutal. It is so savagely brutal -- beheadings, crucifixion, hurtling suspected homosexuals off rooftops to their deaths, locking that downed Jordanian pilot in a cage and then burning him alive -- that even al Qaeda has blanched! That tells you all you need to know about what we're up against now.

Fifth, they have no equal when it comes to mastering social media and the Internet. In the al Qaeda era, recruiting was retail and overt, meaning, terrorists had to recruit would-be terrorists pretty much one at a time and pretty much in the open. We had great success in infiltrating fertile recruiting grounds like mosques and interdicting plots before they went too far. No longer. Now, ISIS recruiting is wholesale and covert.

The vastness of cyberspace allows them to recruit thousands, even millions, all at once, and to do so in the anonymity of people's dens and basements. Likewise, training has gone wholesale and covert. No longer is there the need to travel thousands of miles away to some Afpak training camp. In the infamous words of Inspire magazine, you can be taught on the Internet "how to make a bomb in the kitchen of your mom."

Most worrisome of all is ISIS' tactical approach to terrorism in contrast to that of Al Qaeda and AQAP. While they remain focused on catastrophic attacks, ISIS focuses on what I call "anytime, anywhere, any kind" attacks. ISIS has famously called on its followers to carry out whatever kind of terror attack they can, wherever they are, with whatever they've got: a gun, a knife, a bomb, a car, etc.

While catastrophic attacks, by definition, kill and injure more people than "anytime, anywhere, any kind" attacks, their very scale makes them more complicated to carry out. The more time it takes to plan attacks, the more people are involved in carrying them out, the more money it takes to finance them, etc., the more opportunities there are along the continuum from plot to execution to foil them.

In contrast, there is literally no way of preventing every single would be terrorist from shooting or stabbing the guy next to him, or from mowing down a few people with his car, or from walking into a subway station and igniting a suicide vest.

In short, then, with all due respect to those who rightly see this nation state or that as an increasing threat to the United States, the sobering fact this 9/11 anniversary is that terrorism remains the No. 1 threat.